1. Field of the Invention
The present invention relates to a vibration damping apparatus that constitutes a secondary vibrating system for a vibrating member to be vibration-damped, and that is adapted to reduce vibration of a vibrating member in a primary vibrating system. More particularly, the present invention relates to a vibration damping apparatus of novel construction affording outstanding vibration damping action against low-frequency, large amplitude vibration by a vibrating member of large mass.
2. Description of the Related Art
A dynamic damper composed of a mass-spring system and designed to be attached to a vibrating member of a primary vibrating system, in order to constitute a secondary vibrating system therefor, is known in the art as one type of vibration damping apparatus adapted to reduce vibration in vibrating members whose vibration poses a problem, such as the body of a car. Such an apparatus is disclosed in U.S. Pat. No. 6,991,077, for example.
The frame of a car body may be subjected to input of low-frequency, large amplitude vibration when, for example, the car drives over a bump. Due to the large mass of the car body frame, it will be necessary to use a component of large mass as a mass member, in order to effectively damp such vibration. Given that the mass member has a large mass, it will be necessary to establish a sufficiently low spring constant in order to set the tuning frequency of the secondary vibrating system constituted by the mass-spring system within a low-frequency range.
In typical dynamic dampers employing a compression rubber elastic body as the spring member, is was necessary for the member to have a small cross-sectional area in order to achieve the desired low spring constant. However this arrangement created the problem that it becomes difficult to ensure sufficient support strength for such a mass member of large mass.
It has also been contemplated to use a plate spring made of metal, in order to achieve low spring constant while ensuring adequate support strength.
However, due to the use of mass members having large mass, the use of metal plate springs poses a concern with regard stress concentrations arising in fastening locations to the mass member and to the supporting member (damped member), and to possible fatigue rupture caused thereby. Particularly where a “cantilever structure” by the plate spring for the mass member has been employed, durability of the plate spring will tend to become a greater problem.
In order to alleviate the problem of stress concentration in the plate spring, a “both-sides holding structure” whereby the mass member is supported from both the left and right sides by respective plate springs could also be contemplated. However, where such a both-sides holding structure is employed for the mass member, since the plate springs per se undergo substantially no elongation or contraction in the lengthwise direction, during displacement of the mass member they will not be able to respond to changes in distance between the mass member and the supporting member which are linked by the plate springs. As a result, the linear region of the mass-spring system will be extremely small due to the tensile rigidity of the plate springs in their lengthwise direction, creating the problem of difficultly in achieving the required vibration damping action against low-frequency, large amplitude vibration in particular.
In order to address the problem of stress concentration in the plate spring and of ensuring an adequate linear region, it could be contemplated to employ a sufficient length for the plate springs, for example. However, achieving satisfactory characteristics would require excessive plate spring length dimension, making the dynamic damper much too large for practical purposes, and accordingly this is not an effective solution.